The present invention concerns a tilting vessel for treatment of liquid metal, typically for the gas treatment or filtration of liquid aluminium or magnesium or their alloys, and its sealed connection device with fixed troughs used to feed or evacuate said liquid metal from the vessel.
A vessel for the treatment of liquid metal by gases or filtration or simply for its storage, generally has a capacity of no more than 3 tonnes and comprises feed and outlet devices for the liquid metal. Said liquid metal enters and leaves the vessel continuously, however it is necessary to empty the vessel regularly either in full or in part by tilting about a horizontal axis at an angle which typically lies between 30xc2x0 and 90xc2x0. In addition, the vessel may be provided with a special drainage hole positioned in its lower part.
The outlet device for the liquid metal comprises a port, or tap out, usually provided at the top of one of the vessel walls, extended by a casting spout to pour the liquid metal into a fixed evacuation trough. The feed device for supplying liquid metal from a fixed trough is generally of the same type. Typically the vessel is a rectangular parallelepiped and the tilting axis is parallel to its greatest length. It is essential that the articulated connection between the spout integral with the vessel and the fixed trough should remain impervious to liquid metal at high temperature, despite the repeated cycles of heating and cooling in the installation.
Liquid metal is known to be poured into a fixed trough perpendicular to the axis of horizontal tilting. The latter, usually positioned at the level of the tap out, is then offset outside the vessel and passes through the end common to the spout and trough which are arranged in continuation of one another.
When the vessel is tilted, it is seen that the outlet spout of the said vessel and the fixed trough form a variable angle, and that the connection between these two parts must be articulated and sealed. To achieve the seal of this articulation, a metal knuckle joint is known to be placed on the outside around the ends of the spout and fixed trough, and the inner surface of the said knuckle joint is packed with a lining, which may be graphite-based braided rope, to ensure the seal with the outer surfaces of the spout and the trough. Therefore, when the vessel is tilted, its outlet spout rubs against the lining of the knuckle joint, moving in sealed manner.
When tilted, the vessel provided with this arrangement requires considerable space, in particular when the tilt angle is 90xc2x0, this space requirement being due to the fact that the tilt axis passes through the end of the spout. In addition, metal may freeze in the articulated device, in particular between the metal knuckle joint, the spout and the trough, which complicates and substantially hinders maintenance or dismounting operations.
Also, furnaces for melting and storing liquid metal are known, having a large capacity (several dozen tonnes) which tilt about a horizontal axis and pour the liquid metal into a fixed trough positioned in the continuation of said axis, whose angle of tilt generally does not exceed 10 to 20xc2x0. In this case, a sealed rotating connection between the casting spout integral with the furnace, also positioned on the tilt axis, and the fixed trough of semi-circular section, consists of fitting and adjusting inside the latter the spout that is integral with the vessel which also has a semi-circular section slightly smaller in diameter, and of causing the two semi-circular parts to slide in rotation relative to one another by means of a seal lining, often in graphite-based, placed between the two.
Such device can only be used over small angles of tilt owing to the fact that the lining is pulled as soon as the tilt angle becomes fairly wide. Therefore, this device cannot be applied to treatment vessels, in particular to those which tilt at wide angles. In addition, it is difficult to obtain a good seal owing to the fact that said two parts fitted into one another have different dilation in diametrical direction, that the troughs easily deform after the numerous heat cycles they undergo, and that the clamping force of the lining cannot be adjusted. Moreover, there is a considerable risk of the device becoming blocked on account of the metal which may slide into and freeze inside the interstice between the spout and the trough.
The applicant therefore set out to avoid the above disadvantages and to develop a tilting vessel for treatment with reduced tilt volume which is simultaneously provided with an articulated connection device, between the spout integral with the vessel and the fixed trough, which is perfectly sealed while being of simple design and use (adjustment, maintenance, dismounting, cleaning) and without the possibility of said device causing freezing of the liquid metal.
The invention is a vessel for treating liquid metal, tilting about an axis, fed by a fixed trough and pouring said liquid metal into a fixed evacuation trough, said vessel comprising at least one passage hole for feeding, evacuating or emptying the liquid metal, arranged in one of its walls and extended by a so-called mobile spout integral with the vessel, characterized in that at least the axis of the fixed evacuation trough merges with the tilt axis.
Usually the axis of the feed trough also merges with the tilt axis. It is particularly advantageous to provide this arrangement for vessels which tilt at an angle greater than 30xc2x0 which may reach 90xc2x0.
Generally, the vessel is at least approximately a rectangular parallelepiped, its walls possibly being slightly tapered, and the tilt axis is parallel to its greater length, that is to say parallel to the longer walls and perpendicular to the shorter walls.
Said tilt axis preferably passes through an upper angle of said shorter walls; in this case, it not only merges with the axes of the fixed troughs and mobile casting or feed spouts, but also with those of the casting or feed holes. But it may very well be located at another point of the vessel or even offset outside the vessel; in this case it again merges with the axes of the fixed troughs and mobile spouts.
According to the invention, the ends of the mobile spouts and fixed troughs having a circular section, aligned along the tilt axis, are linked by a connection device articulated in rotation about said axis, impervious to liquid metal, able to rotate at an angle of more than 30xc2x0 which may reach 90xc2x0 without losing its seal properties and thereby allowing full or partial emptying of the vessel.
Said device articulated in rotation according to the invention comprises:
an adapter flange secured to the end of the spout, centred over the tilt axis, comprising a circular seal bearing whose plane is perpendicular to said axis,
a connection flange secured to the end of the fixed trough, centred over the tilt axis, comprising a circular seal bearing whose plane is perpendicular to said axis, facing and co-operating with the preceding seal bearing;
at least one seal resistant to heat and liquid metal positioned between the two bearings;
a clamp device, optionally supported by a fixed part, used to adjust and maintain the clamping of the flanges relative to one another to ensure the sealed connection while allowing said flanges to pivot relative to one another.
Preferably two graphite-based seals are provided, one fixed to the bearing of each flange, which rub against one another.
The mobile spout and fixed trough being positioned in continuation one after the other so that the bearings of the seals which face one another correspond perfectly, it is advantageous to place centering means on each of the flanges which co-operate together and may form a centering device.
Therefore one of the flanges may comprise a cylindrical projection at whose end the seal bearing may be placed; this circular projection, like the flange, is designed so that it slide fits into a corresponding housing positioned on the other flange at the bottom of which the other seal bearing may be placed so that it faces the bearing of the first flange. It is seen that these two parts, by fitting into one another, ensure the centering of the seal bearings.
To achieve the liquid metal seal, while maintaining an appropriate friction force to enable the rotation of one flange relative to the other, all that is needed is to tighten the two seals against each other using the clamp device. To prevent the fixed trough from being pulled when the spout rotates, it is advantageous to reinforce its immobilisation in the vicinity of the connection flange, for example by means of reinforcement bars integral with a frame.
The clamp device may comprise screw tie rods supported firstly by one of the support parts integral with the frame, either fixed or preferably manoeuvrable, and secondly on the connection flange via elastic parts, for example springs or cambered washers of xe2x80x9cbellevillexe2x80x9d type. Nuts are used to adjust the clamping force by compressing the elastic parts as required. The elastic parts also enable the seal to be maintained during heat cycles by absorbing the dilatations.
It can be seen that with this kind of device, in which the dilatations occur in the axis, it is possible to overcome recurrent or endemic deformations due to the heat cycles to which the unit is subjected during stoppage and re-start up of the vessel, and to achieve the desired seal while preventing any undue leakage or freezing of the liquid metal which could hinder vessel operation. Also, to dismount the device for its cleaning or maintenance (for example to change the seals) all that is required is to draw the two flanges away from one another.
To facilitate dismounting, it is also possible to extend the connection flange by a portion of fixed trough secured to the actual fixed trough by means of a rigid fixing device (for example using flanges integral with the trough and the portion of trough, bolted together) that is sealed, easy to dismount and accessible, and to lay the entire unit (portion of fixed trough, connection flange, clamp device) on a mobile carriage which also carries the support frame for the clamp device. To dismount, the fixed trough only needs to be uncoupled from the portion of trough and the latter can then be drawn away, with its connection flange, from the mobile spout fitted with its adapter flange after releasing the clamp device.
The flanges are generally in steel or refractory cast iron; the inside of the portion of fixed trough may be lined with the same refractory product as the spouts, troughs or vessel for liquid metal.
The device of the invention applies to the connection of the liquid metal vessel to its evacuation trough as well as to its feed trough. When it applies to both, the latter are positioned on the same axis, as described above.
The invention also concerns vessels for liquid metal comprising one or more articulated connection devices, and the processes which use the vessels or said devices according to the invention. These processes are in particular filtration or gas treatment of liquid metals such as aluminium, magnesium or their alloys.